Vehicle engines may be downsized to conserve fuel and reduce engine emissions. Smaller engines may operate more frequently at higher intake manifold pressures as compared to larger engines in the same vehicle. Engine pumping losses may be reduced by operating an engine with higher intake manifold pressures, but the opportunities to provide engine vacuum to the vehicle vacuum system may be reduced. Some attempts to increase vacuum production have included ejectors, ways of advantageously controlling engine throttle position, and various other control strategies. However, many of these systems and methods require hardware that is additional to more conventional engines. Consequently, vehicle cost may be higher for such systems.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating a vehicle powertrain, comprising: reducing torque delivered from an engine to vehicle wheels via reducing a torque transferred via a clutch in response to a request for increased vacuum.
At very low vehicle speed (e.g. less than 6 to 10 kph), torque or force produced by a vehicle engine tends to purposefully accelerate a vehicle while the operator's foot is off the accelerator pedal. This is called creep force. By reducing an amount of engine torque that is provided to vehicle wheels (creep torque) when no driver demand torque is present, it may be possible to provide a technical result of an engine providing an increased amount of vacuum for vacuum consumers. For example, if an engine is operating at idle speed and X Nm of torque is provided by the engine to vehicle wheels to maintain a positive torque at the wheels, it may be possible to reduce engine torque from X Nm to Y Nm while continuing to operate the engine at the same idle speed such that additional intake manifold vacuum is produced. In particular, since less engine torque is used to operate the engine at Y Nm than at X Nm, the engine can operate using a reduced air charge, and the reduced air charged is provided via throttling the engine and allowing less air into the engine intake manifold so that intake manifold pressure is reduced and vacuum is increased. In this way, the desired technical result of providing additional vacuum may be achieved.
The present description may provide several advantages. Specifically, the approach may improve an amount of vacuum available for a vehicle. Further, the approach may not be noticeable to a driver. In addition, the approach may reduce an amount of time that it takes an engine to produce a desired amount of vacuum.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.